Method of pickling without mottling due to gas bubble retention



March 29, 1966 G. A. BAKER 3,243,317

METHOD OF PICKLING WITHOUT MOTTLING DUE TO GAS BUBBLE RETENTION Filed April 19, 1963 0 9 Q Q O 0% 1 0 0 0 0 0 0 0 0 0 0 o I: Q o o 0 O0 :3 H6. 3,

INVENTOR. GLENN A. BAKER ZQM'W United States Patent Ofifice 3,243,317 Patented Mar. 29, 1966 3 243,317 METHOD OF PICKLTNG WITHOUT MOTTLING DUE TO GAS BUBBLE RETENTION Glenn A. Baker, Muskegou, Mich., assignor to C01! Anodizers, Inc., Muskegon, Mich., a corporation of Michigan Filed Apr. 19, 1963, Ser. No. 274,107 2 Claims. (Cl. 134-15) This invention relates to improvements in metal brightening baths, and more particularly to a guide roller surface configuration which eliminates entrapment of gas bubbles and consequent spotting of a metal strip as it is drawn through a brightening bath.

In the manufacture of certain products such as anodized aluminum, a strip of metal unwound from a storage roll is continuously fed through a chemical reagent bath to pickle the metal, i.e. remove all traces of oxide and surface impurities from the metal just before it is treated with surface conditioning methods such as anodizing. The pickling bath for these purposes may vary in composition depending on the result sought to be achieved; for example, it may be composed of a mixture of phosphoric and nitric acid, or it may be a caustic fluid. In each instance, however, the reagent is usually at an elevated temperature, and the chemical reaction with the metal strip is very active. In particular, the reaction generates large quantities of gas which are prevented from adhering to the metal strip by subjecting the reagent to strong agitation. This agitation is so energetic, however, that the strip has to be threaded over a guide roller in the bath to prevent it from being subjected to damaging random lateral motion in the bath. It has been found that in the operation of such apparatus, gas bubbles became entrapped bet-ween the strip and the guide roller at the point where the strip engaged the guide roller and were entrained between the guide roller and the strip throughout the arc of contact between the guide roller and the strip. Although the time involved in this entrapment was rather small, the extremely strong action of the reagent around the bubbles was sufficient to give the strip surface an undesirable mottled appearance.

The present invention solves this problem by providing the surface of the guide roller with a pattern of closely spaced raised areas and depressions in which the depressions gather the gas bubbles which would otherwise become entrapped between the strip and the roller and thus keep them space-d from the surface of the metal.

It is therefore the object of this invention to provide a surface configuration for guide rollers in gas-generating metal strip cleaning baths which will hold entrapped gas bubbles spaced from the surface of the metal strip during engagement of the strip with the roller.

It is another object of the invention to provide a surface configuration of the type described in which entrapped gas bubbles are continuously biased toward the axial extremities of the roller.

These and other objects of this invention will become apparent from the following specification, taken in connection with the accompanying drawings in which:

FIG. 1 is a diagrammatic view showing the environment of the invention;

FIG. 2 is a front elevation of one embodiment of roller according to this invention;

FIG. 3 is a front elevation of another embodiment of roller according to this invention; and

FIG. 4 is a vertical section along line IVIV of FIG. 3.

Basically, the invention consists in providing spaces between the metal strip and the guide roller into which gas bubbles formed on the metal strip can escape while the strip is in contact with the roller." For this purpose, the strip is preferably supported by narrow, preferably circumferentially discontinuous ridges or raised areas whose width is suflicient only to properly support the strip without wearing too easily. At the same time, the stripengaging ridge surface should be sufficient to prevent the lateral movement of the strip which the roller is designed to prevent.

In FIG. 1, the strip 10 of aluminum or the like is shown being fed through a cleaning bath consisting of a stainless steel vat 12 filled with a reagent 14. Appropriate means (not shown) are provided to agitate the reagent 14 and to maintain it at an elevated temperature. The strip 10 is drawn through the bath 14 in the direction of the arrows 16 by drive rollers 18, 20. The strip is guided through the bath by stainless steel guide roller 22 which is shown in greater details in FIGS. 2 through 4.

FIG. 2 shows an embodiment of the roller 22 in which spiral ridges 24 define spiral depressions 26. The spirals 24, 26 are directed axially outwardly from each side of the center line 28 so that if the cylinder of FIG. 2 is rotating in a counterclockwise direction as seen from the left in FIG. 2, any gas bubbles entrapped in the depressions 26 will be centrifugally biased toward the axial ends of the roller 22. In a preferred embodiment, the ridges 24 may be about /s of an inch wide, the depressions 26 may be of the same width, and the depth of the depressions 26 may also be Me of an inch. As a further refinement, the crests of the ridges 24 may be somewhat rounded in shape to facilitate escapement of bubbles into the depressions 26.

FIG. 3 shows an alternative embodiment of the invention in which the ridges are not continuous, but instead are formed as raised surfaces in the shape of small diamonds. In this embodiment, more reliance is placed on the radial escapement of any entrapped bubbles during the portion of the revolution of roller 22 when it is out of contact with strip 10, but the roller surface contacting the strip 10 is less than in the embodiment of FIG. 2 so that better brightening action is obtained.

In the alternative, it is equally possible to overlay the flat surface of the cylinder 22 with a coarse mesh stainless steel screen (not shown), or to use any other means which carry out the concepts of the invention of providing alternate raised and depressed areas in sufficiently close spacing to support the strip and yet allow room for the gas bubbles to become spaced from the surface of the strip.

Obviously, the method of this invention can be carried out in many different ways, and we therefore do not desire to be limited except by the scope of the following claims.

I claim:

1. The method of continuously pickling metal strip without mottling caused by irregular pickling due to gas 'bubble retention on the strip surface comprising the steps of: providing a pickling bath; continuously passing metal strip down into the pickling bath and thereby generating gaseous bubbles with the reaction caused thereby; passing said strip around a guide roller immersed in the bath; continuously removing the generated gaseous bubbles from the strip surface between the strip and the roller and receiving them in spaced cavities on the surface of the 2. The method of continuously pickling aluminum strip without mottling of the surface caused by irregular pickling comprising the steps of: providing a pickling bath; providing a guide roller in said pickling bath, with spaced gaseous receiving cavities on its surf-ace and alternate strip support areas; supporting the roller immersed in the pickling bath; passing an aluminum strip into the pickling bath to pickle the same and thereby generate gaseous bubbles; passing the strip around the roller while simultaneously removing from the surface of the strip between the strip and the roller gaseous bubbles generated by pickling, and receiving these gaseous bubbles into the cavities on the roller to remove them from contact with the strip surface, and removing the strip from the pickling bath.

1,975,708 10/1934 Bleibler 13416 X 2,004,267 6/1935 Brockway 118-419 X 2,176,835 10/1939 Cumfer 118-419 X 2,257,410 9/1941 Arentsen 118419 X 2,309,585 1/1943 Haddock 118419 X 2,474,717 6/ 1949 Belcher 13464X 3,056,164 10/1962 Reichel et a1 134-15 X CHARLES A. WILLMUTH, Primary Examiner.

JOSEPH SCOVRONEK, Examiner.

15 R. L. BLEUTGE, J. ZATARGA, Assistant Examiners. 

1. THE METHOD OF CONTINUOUSLY PICKLING METAL STRIP WITH MOTTLING CAUSED BY IRREGULAR PICKLING DUE TO GAS BUBBLE RETENTION ON THE STRIP SURFACE COMPRISING THE STEPS OF: PROVIDING A PICKLIN BATH; CONTINOUSLY PASSING METAL STRIP DOWN INTO THE PICKLING BATH AND THEREBY GENERATING GASEOUS BUBBLES WITH THE REACTIONCAUSED THEREBY; PASSING SAID STRIP AROUND A GUIDE ROLLER IMMERSED IN THE BATH; CONTINUOUSLY REMOVING THE GENERATED GASEOUS BUBBLES FROM THE STRIP SURFACE BETWEEN THE STRIP AND THE ROLLER AND RECEIVING THEN IN SPACED CAVITIES ON THE SURFACE OF THE ROLLER, AND THE PASSING THE STRIP UP OUT OF THE PICKLING BATH. 